The present invention relates to thermocouples which are used in conjunction with printed circuit boards for training personnel in soldering/desoldering of leads of circuit components to the printed circuit boards, as well as for conducting a quantitative analysis of the performance of repair, rework, and production equipment used for soldering/desoldering, cleaning, preheating, and spot-welding of components mounted to printed circuit boards. In particular, the invention relates to the formation of thermocouples for such purposes by standard printed circuit board construction techniques, as opposed to standard thermocouple construction techniques, as well as the manner in which they can be made and used to emulate or simulate a wide variety of circuit board types, layouts and assembly configurations.
In commonly owned U.S. Pat. No. 4,224,744, circuitry for teaching soldering and a practice circuit board for use therewith are disclosed, wherein a training board having a plurality of terminals thereon and wherein a plurality of temperature sensing devices associated with the respective terminals are provided at each terminal where the soldering of a joint is attempted to monitor the performance of a trainee or other person whose repair skills are being evaluated. One form of temperature sensing means that is disclosed is the provision of thermocouples at each of a plurality of through holes formed in a printed circuit board. These thermocouples are comprised of a first conductor, such as electroless copper, that is plated through the holes so as to form pads or lands at each of opposite sides of the printed circuit board, and a metal foil or wire made of iron or constantan or some other dissimilar conductor metal from that of the plated through hole that is attached to one of the pads or lands of the plated through conductor, whereby a thermocouple junction is formed. For formation of these thermocouple junctions, the use of electrical arc, flame heating, soldering, swagging, welding, brazing, beading, or butt-welding techniques are disclosed. Furthermore, while this patent indicates that its disclosure is also applicable to desoldering, welding, etc., as well as to circuit connections other than those on a single or double-sided printed circuit board, such as multilayer boards, ceramic printed circuits, etc., and various terminations such as plated through holes, unsupported holes, funnelets, eyelets, standoffs, etc., no structures, techniques or applications are disclosed which are either directed to the emulation or simulation of a wide assortment of circuit board layouts, types and assembly configurations which vary by component type, substrate material, thermal characteristics and other factors, or to the application thereof to the development, evaluation, monitoring and adjustment of "thermally affecting" production, rework or repair processes and equipment used therefor, i.e., for soldering/desoldering, preheating, spot-welding, etc.
Commonly owned U.S. Pat. No. 4,224,744 also discloses in detail the various factors which impact upon the ability to perform high quality rework and repair operations upon electronic assemblies, and this description is hereby incorporated by reference for the sake of brevity. These factors include not only the human factor, for which training to obtain the requisite skills and experience to enable the operator to observe the work and react appropriately in the manipulation of the soldering iron or other rework and repair device is the best insurance, but also includes other factors which are not operator dependent, such as the characteristics of the rework and repair device, e.g., a soldering iron for which its idle tip temperature, recovery rate, etc., and characteristics of the component and printed circuit board, such as temperature, thermal conductivity, specific heat, etc. As a result, for proper training and evaluation of personnel, it is desirable to be able to simulate as realistically as possible a wide range of circumstances an operator is likely to encounter. Also, even with the best of training, the potential exists for overheating the work, as a result of excessive dwell times or temperatures, so as to cause printed circuit board damage in the form of lifted pads, damage to plated through holes, or, in extreme cases, damage to the fiberglass laminate, etc., as a result of equipment related factors. Thus, it is also desirable to provide a means by which new equipment can be evaluated, particularly automatic equipment, through analysis of the temperature profile that, for example, a soldered joint is exposed to during, for example, a soldering/desoldering process.
The normal method of soldered joint inspection is visual. However, such a qualitative method of analysis is ineffective since the physical appearance of a soldered joint, after it has been made, gives no real indication of the maximum temperature that the joint achieved or how long it was maintained at that temperature. On the other hand, to obtain a quantitative analysis of the temperature conditions to which a joint is subjected, thermocouples have to be attached to the circuit pads and/or component leads, so that temperatures can be recorded utilizing a computer data logging system. However, attaching thermocouples to leads or pads, usually done by spot welding, is a difficult task, and if multiple joints are to be analyzed, the task becomes cumbersome and expensive as each thermocouple costs approximately $5.